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It wraps open-coded kref_get_unless_zero() and asserts that dma_list_mutex is held, matching its put counterpart. No functional change intended. Suggested-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg --- drivers/dma/dmaengine.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 9049171df857..cb3b7bccce1f 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -433,6 +433,12 @@ static void dma_device_release(struct kref *ref) device->device_release(device); } =20 +static int __must_check dma_device_get(struct dma_device *device) +{ + lockdep_assert_held(&dma_list_mutex); + return kref_get_unless_zero(&device->ref); +} + static void dma_device_put(struct dma_device *device) { lockdep_assert_held(&dma_list_mutex); @@ -460,8 +466,7 @@ static int dma_chan_get(struct dma_chan *chan) if (!try_module_get(owner)) return -ENODEV; =20 - ret =3D kref_get_unless_zero(&chan->device->ref); - if (!ret) { + if (!dma_device_get(chan->device)) { ret =3D -ENODEV; goto module_put_out; } --=20 2.43.0 From nobody Mon Aug 24 05:24:40 2026 Received: from DM1PR04CU001.outbound.protection.outlook.com (mail-centralusazon11010048.outbound.protection.outlook.com [52.101.61.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8158D399001; 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Sat, 22 Aug 2026 14:22:17 -0500 From: Shivank Garg Date: Sat, 22 Aug 2026 19:22:04 +0000 Subject: [PATCH v5 2/4] dmaengine: Fix device kref underflow in dma_chan_put() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20260822-dmaengine-kref-fix-v5-2-d4a4ee47d927@amd.com> References: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@amd.com> In-Reply-To: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" , Andrew Morton CC: , , , Shivank Garg , Frank Li X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787426532; l=1642; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=UiUCtXvQIMfoyyI7A1JkRSEb8TYGQYCOz3ZIZD85bdM=; b=rNtsNNwQiQ9lRVAQ/8PtBe/+63Pj1K00qQJkPpSh3riSHmNfUfMePaARwwiCRpzf1sa7yaRbX AOJPItzCVELCs8jfSE1NVO8usJP2a2a5beomywb4YiSl1tczU8e1+KU X-Developer-Key: i=shivankg@amd.com; 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chan->client_count++; return 0; } if (!try_module_get(owner)) return -ENODEV; if (!dma_device_get(chan->device)) { // calls kref_get_unless_zero() dma_chan_put() drops the ref unconditionally, so every fast-path get/put pair drops one extra device reference. The bug fires when two conditions hold together: a non-private provider has a persistent client holding chan->client_count > 0 and another client cycles dmaengine_get()/dmaengine_put(). When the kref hits zero, the subsequent dma_find_channel() returns NULL even though the provider module is still loaded. Fix this by dropping device->ref only on the last put, matching the single slow-path get. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struc= t") Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg --- drivers/dma/dmaengine.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index cb3b7bccce1f..f2760b039d93 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -520,7 +520,9 @@ static void dma_chan_put(struct dma_chan *chan) chan->route_data =3D NULL; } =20 - dma_device_put(chan->device); + /* This channel is not in use anymore, drop the device ref */ + if (!chan->client_count) + dma_device_put(chan->device); module_put(dma_chan_to_owner(chan)); } =20 --=20 2.43.0 From nobody Mon Aug 24 05:24:40 2026 Received: from SA9PR02CU001.outbound.protection.outlook.com (mail-southcentralusazon11013045.outbound.protection.outlook.com [40.93.196.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84405371889; 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Sat, 22 Aug 2026 14:22:20 -0500 From: Shivank Garg Date: Sat, 22 Aug 2026 19:22:05 +0000 Subject: [PATCH v5 3/4] dmaengine: fix use-after-free in dma_chan_put() and dma_release_channel() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-ID: <20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com> References: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@amd.com> In-Reply-To: <20260822-dmaengine-kref-fix-v5-0-d4a4ee47d927@amd.com> To: Vinod Koul , Frank Li , "Logan Gunthorpe" , Andrew Morton CC: , , , Shivank Garg , Sashiko , Frank Li X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787426532; l=1931; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=QMCEnZtwHAzn8E8PmGPgLxGc/LdJXZ5sh7KxsGFDltI=; b=KgjU5RuicuFEyYxZ6qd5M4AyXQot4ng0gZS+uSFvEHOCqBaQ+uDsPDERHc+QA7hoXtUV0ei+7 FpthQZyyG8CAo0+qOeMlpR39hLdT9d/VwK79Z0pcL9pinctO93W0ptv X-Developer-Key: i=shivankg@amd.com; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: M1KpWGkHUVH85T0eEVtau13yvDzI53MAXM9EakhMDYhDkx/vLjex+uhIsDz+LomKXHHiaArsJnHX2qWmzH5B7NZWRp9CC/MAu6JS2WIgUcmmkOUCU8NpybY4u7xoBhi8too4ZQIc8oVdkjaxwFgSolqBVBdsovKI6q6xc3yf+wV7oHu4r4irk/0d0fvveZhfeu5i1aOvUmqiYRM1quy3YuY8qkaGMveMc4cOAPGMx+Ca1xFYZoIHliLouwe78aPfl8paDcoWU5wFeQtOjWw34eiHVoIIKvVJrp+bNpJ+j4WcAeJmKQoOZyiSoc/ESKCi/fLVPomMdFx6s3FFpCIUX27OE8YK3T5PL5sCUX/d22OdOO7f+xJH+NHt6piIzSihyNhGgYtZEr2QATqM2+s7hzmivXWPfZ1zFHPAEMNn5XmrFTWl2qNG6sRSSq+g86lj X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Aug 2026 19:22:23.5364 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 52f6646e-646f-464f-3072-08df0082b1ae X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BY1PEPF0001AE17.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4474 When dma_device_put() drops the last reference on chan->device->ref, dma_device_release() runs and may free the dma_device along with its channels. dma_chan_put() then still reads chan->device->owner via dma_chan_to_owner() for the trailing module_put(). KASAN catches it: slab-use-after-free in dma_chan_put+0x3e6/0x4c0 Read of size 8 by task insmod/6319 Freed by task 6319: kfree+0x225/0x470 dma_chan_put+0x395/0x4c0 dmaengine_put+0xf8/0x160 Cache the module owner in dma_chan_put() before the put so the trailing module_put() does not need chan->device. Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struc= t") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d612= 5048fb7@amd.com Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg --- drivers/dma/dmaengine.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index f2760b039d93..9214b9272a55 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -500,10 +500,13 @@ static int dma_chan_get(struct dma_chan *chan) */ static void dma_chan_put(struct dma_chan *chan) { + struct module *owner; + /* This channel is not in use, bail out */ if (!chan->client_count) return; =20 + owner =3D dma_chan_to_owner(chan); chan->client_count--; =20 /* This channel is not in use anymore, free it */ @@ -523,7 +526,7 @@ static void dma_chan_put(struct dma_chan *chan) /* This channel is not in use anymore, drop the device ref */ if (!chan->client_count) dma_device_put(chan->device); 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a=ed25519-sha256; t=1787426532; l=2079; i=shivankg@amd.com; s=20260518; h=from:subject:message-id; bh=xaddx9darcAdVHfugBdf0HJWW1q15PBK4nA8kesfv6w=; b=NWq/cpEP4qvVM7Jq5FO+NAZJx+9fOlrBfiefbcsOXHD9wbEjGnTrlYWq0DTcIqNmWIR/U3yxu Fe1bGr3IrouAFd4Hl4TFGYgMFUOsMFu6or9P8hKJ8WpHJByL4Kb5Uf3 X-Developer-Key: i=shivankg@amd.com; a=ed25519; pk=2l2QGTeXuGkZTtfmx0nPQU8iFZfjYmX/ymMojitevx4= X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY1PEPF0001AE1A:EE_|IA0PR12MB9012:EE_ X-MS-Office365-Filtering-Correlation-Id: f36ff150-c11f-4a99-b658-08df0082b3b1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|23010399003|1800799024|36860700016|376014|56012099006|10067099003|22082099003|18002099003|11063799006|13003099007; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(82310400026)(23010399003)(1800799024)(36860700016)(376014)(56012099006)(10067099003)(22082099003)(18002099003)(11063799006)(13003099007);DIR:OUT;SFP:1101; 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Because there is no grace period between unlinking the device and freeing it, concurrent RCU readers in dma_issue_pending_all() can access the device after it has been freed. The lockless walk originally relied on clients holding a dmaengine reference to pin the provider module, and therefore the device, for as long as they might traverse the list. Commit 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct") decoupled the dma_device lifetime from the module reference, so the device can now be released while a reader is still walking the list. Add synchronize_rcu() before the device is freed, so RCU readers are guaranteed to have finished. Keep it unconditional: providers that do not implement device_release() free the device themselves once dma_async_device_unregister() returns. This call will delay for a grace period with dma_list_mutex held, which is safe and only teardown path is delayed. Fixes: 2ba05622b8b1 ("dmaengine: provide a common 'issue_pending_all' imple= mentation") Suggested-by: Sashiko Link: https://sashiko.dev/#/patchset/20260526-dmaengine-kref-fix-v2-0-3df60= afac01d@amd.com Reviewed-by: Frank Li Reviewed-by: Logan Gunthorpe Signed-off-by: Shivank Garg --- drivers/dma/dmaengine.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 9214b9272a55..f9bc3e69fe58 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -428,6 +428,7 @@ static void dma_device_release(struct kref *ref) =20 list_del_rcu(&device->global_node); dma_channel_rebalance(); + synchronize_rcu(); =20 if (device->device_release) device->device_release(device); --=20 2.43.0